Organic electroluminescence (hereinafter referred to as xe2x80x9cELxe2x80x9d) display panels using organic EL elements have been known as flat panel displays. While liquid crystal displays (LCDs) are widely used as flat panel displays, LCDs merely transmit or reflect light from a light source separately provided, and are not self-emissive. On the other hand, organic EL display elements are used in a self-emissive display for supplying a current to an organic EL layer provided between an anode and a cathode to cause the layer to emit light, and therefore back lighting is not required, as opposed to the LCDS. Organic EL display devices are expected to become the next mainstream flat display panel for that reason and because they are thin, compact, bright, and low power consumption devices. Particularly, it is expected that an active matrix organic EL displays including a switching element for each pixel will become mainstream devices among next-generation flat panel display devices because each pixel thereof can be independently turned on and the amount of current can be decreased, making it possible to maintain a high display quality when used for high resolution large screens.
In such an active matrix organic EL display, a thin film transistor provided for switching for each of the organic EL elements (light emissive elements) arranged in a matrix individually controls supply of current from a power source to the organic EL element, and causes the element to emit light at a luminance in accordance with a data signal.
Known thin film transistors used as a switching element for each pixel include a semiconductor layer of amorphous silicon, polysilicon, or the like, which forms an active layer. Although for simplicity in manufacturing amorphous silicon has been used for the active layer of the thin film transistor, polycrystalline silicon has come to be used in order to enhance operation speed and implement a display device with a high resolution. To form a polysilicon layer on a substrate having a low melting point, a laser annealing process is first performed on a silicon film formed in the amorphous state, thereby polycrystallizing the amorphous silicon.
Such a laser annealing process is usually performed by sequentially scanning the irradiated object with a pulsed laser beam (sheet beam) shaped such that the irradiated area will be an elongated rectangle. However, as the laser irradiating conditions are varied and not always the same, resulting variation in crystal properties of the thin film transistors leads to a difference in properties among the thin film transistors located at different positions on the same substrate, resulting in variations in pixel luminance.
A semiconductor device having on a substrate a plurality of thin film transistors using a semiconductor layer annealed with a line pulsed laser as a channel region, includes: at least one element driving thin film transistor for supplying a driving current from a power source line to a corresponding driven element; and a switching thin film transistor for controlling the element driving thin film transistor based on a data signal supplied when selected; wherein the element driving thin film transistor is disposed such that a longitudinal direction of an area irradiated with the line pulsed laser traverses the element driving thin film transistor in a channel width direction thereof.